1. Field of the Invention
The present invention relates to an improved gyroscope; more particularly, the invention relates to a gyroscope having at least one piezoelectric crystal and preferably a self-aligning gyroscopic element.
2. Description of the Related Art
Gyroscopes are known which comprise a gyroscopic element, also called a flywheel, and a spin motor. Such gyroscopes are disclosed to have two piezoelectric crystals mounted radial to the motor spin axis of the gyroscopes. The crystals are aligned at 180.degree. apart, restrained on one end at the hub, and restrained by the gyroscopic element at a radially extending outer end. Such features are disclosed in the art, such as FIG. 1 of U.S. Pat. No. 4,601,205 and FIG. 5 of U.S. Pat. No. 4,311,046. The '046 patent also discloses that it is known to make a gyroscope with a flywheel attached to a base via flexible hinges.
U.S. Pat. No. 4,211,951 discloses a shear-type pre-stressed piezoelectric force transducer. This article comprises two piezoelectric elements parallel to the spin axis.
U.S. Pat. No. 4,621,529 discloses multi-sensor pickoff assembly including a gyroscopic element which has a spin axis. The assembly has a flexure hinge for resiliently mounting the element on the base. There is a piezoelectric beam which is mounted in a coaxial relation to the spin axis. The piezoelectric beam is adapted to generate an electrical signal proportional to the angular velocity of the navigation sensor about an axis perpendicular to the spin axis. There are means to restrain the piezoelectric beam in place. The piezoelectric beam is restrained between the base and the gyroscopic element. The gyroscopic element is maintained in place at the base by a keeper means which can include a pin perpendicular to the spin axis and restrained on either end with the piezoelectric element attached to the center of the pin.
In U.S. Pat. No. 4,715,227 which is commonly assigned and commonly invented with the '529 patent, the '529 is characterized as having had problems during operation. The embodiment having a trapezoidal shape piezoelectric beam was indicated to have two problems. The first problem arose due to the fact that the clamps in the piezoelectric crystals had different coefficients of expansion, thereby causing a mismatch to exist between the two different materials. Consequently, the piezoelectric beam tended to crack. The second problem found was that vibrations from the spindles and bearings of the multi-sensor assembly were transmitted to the gyroscopic element. These vibrations were in turn transmitted to the piezoelectric crystal beam resulting in a large amount of noise. This limited the performance of the assembly.
U.S. Pat. No. 4,715,227 disclosed a multi-sensor assembly with angular rate piezoelectric crystal beam mounted coaxial to the spin axis. In this assembly the crystal was in diamond shape. The crystal was held between the gyroscopic element and the base. It was trussed in the gyroscopic element between three wires perpendicular to the spin axis and in the base by a fourth wire, also perpendicular to the spin axis. Each of the wires was restrained at their ends and the piezoelectric crystal was secured intermediate of the ends of the wires between each wire, with each wire located at the point of the diamond shaped crystal. This gyroscope contained flexible hinges between the gyroscopic element and the base.
U.S. Pat. Nos. 4,197,737; 3,359,806; and 3,142,991 are cited as being of interest
Small gyroscopes are known and desired in the art. Reference is made to Miller Small Two-Axis Sensor Has Multiple Uses, Aviation Week & Space Technology, Aug. 8, 1966, and Litton, A gyro this small? Really?. The Litton gyroscope is disclosed to be 0.910 inches in axial length and about 0.750 inches in diameter perpendicular to the spin axis.
As the above references indicate, there is a need for relatively small gyroscopes. However, in making gyroscopes small, care must be taken to be sure that precision and accuracy are maintained and improved. Additionally, it is desirable to manufacture small precision parts uniformly and economically.